title: Single-material zinc sulfide bi-layer antireflection coatings for GaAs solar cells.
abstract: We demonstrated the efficiency improvement of GaAs single-junction (SJ) solar cells with the single-material zinc sulfide (ZnS) bi-layer based on the porous/dense film structure, which was fabricated by the glancing angle deposition (GLAD) method, as an antireflection (AR) coating layer. The porous ZnS film with a low refractive index was formed at a high incident vapor flux angle of 80° in the GLAD. Each optimum thickness of ZnS bi-layer was determined by achieving the lowest solar weighted reflectance (SWR) using a rigorous coupled-wave analysis method in the wavelength region of 350-900 nm, extracting the thicknesses of 20 and 50 nm for dense and porous films, respectively. The ZnS bi-layer with a low SWR of ~5.8% considerably increased the short circuit current density (J(sc)) of the GaAs SJ solar cell to 25.57 mA/cm(2), which leads to a larger conversion efficiency (η) of 20.61% compared to the conventional one without AR layer (i.e., SWR~31%, J(sc) = 18.81 mA/cm(2), and η = 14.82%). Furthermore, after the encapsulation, its J(sc) and η values were slightly increased to 25.67 mA/cm(2) and 20.71%, respectively. For the fabricated solar cells, angle-dependent reflectance properties and external quantum efficiency were also studied.
authors.forename: Jung Woo
authors.initials: JW
authors.lastname: Leem
authors.forename: Dong-Hwan
authors.initials: DH
authors.lastname: Jun
authors.forename: Jonggon
authors.initials: J
authors.lastname: Heo
authors.forename: Won-Kyu
authors.initials: WK
authors.lastname: Park
authors.forename: Jin-Hong
authors.initials: JH
authors.lastname: Park
authors.forename: Woo Jin
authors.initials: WJ
authors.lastname: Cho
authors.forename: Do Eok
authors.initials: DE
authors.lastname: Kim
authors.forename: Jae Su
authors.initials: JS
authors.lastname: Yu